An internal combustion engine of the type mentioned in the introduction may be used as a motor vehicle drive. Within the context of the present disclosure, the expression “internal combustion engine” encompasses diesel engines and Otto-cycle engines and also hybrid internal combustion engines, which utilize a hybrid combustion process, and hybrid drives which comprise not only the internal combustion engine but also an electric machine which can be connected in terms of drive to the internal combustion engine and which receives power from the internal combustion engine or which, as a switchable auxiliary drive, additionally outputs power.
In recent years, there has been a trend in development toward supercharged engines, wherein the economic significance of said engines for the automobile industry continues to steadily increase.
Supercharging is primarily a method for increasing power in which the air needed for the combustion process in the engine is compressed, as a result of which a greater air mass can be fed to each cylinder in each working cycle. In this way, the fuel mass and therefore the mean pressure can be increased.
Supercharging is a suitable means for increasing the power of an internal combustion engine while maintaining an unchanged swept volume, or for reducing the swept volume while maintaining the same power. In any case, supercharging leads to an increase in volumetric power output and a more expedient power-to-weight ratio. If the swept volume is reduced, it is thus possible to shift the load collective toward higher loads, at which the specific fuel consumption is lower. By means of supercharging in combination with a suitable transmission configuration, it is also possible to realize so-called downspeeding, with which it is likewise possible to achieve a lower specific fuel consumption.
Supercharging consequently assists in the constant efforts in the development of internal combustion engines to minimize fuel consumption, that is to say to improve the efficiency of the internal combustion engine.
For supercharging, use may made of an exhaust-gas turbocharger, in which a compressor and a turbine are arranged on the same shaft. The hot exhaust-gas flow is fed to the turbine and expands in the turbine with a release of energy, as a result of which the shaft is set in rotation. The energy released by the exhaust-gas flow to the turbine and ultimately to the shaft is used for driving the compressor which is likewise arranged on the shaft. The compressor conveys and compresses the charge air fed to it, as a result of which supercharging of the cylinders is obtained. A charge-air cooler may be arranged in the intake system downstream of the compressor, by means of which charge-air cooler the compressed charge air is cooled before it enters the at least one cylinder. The cooler lowers the temperature and thereby increases the density of the charge air, such that the cooler also contributes to improved charging of the cylinders, that is to say to a greater air mass. Additional compression by cooling may take place.
The difference between an exhaust-gas turbocharger in relation to a supercharger—which can be driven by means of an auxiliary drive—consists in that an exhaust-gas turbocharger utilizes the exhaust-gas energy of the hot exhaust gases, whereas a supercharger draws the energy needed for driving it directly or indirectly from the internal combustion engine and thus adversely affects, that is to say reduces, the efficiency, at least for as long as the drive energy does not originate from an energy recovery source. Thus, the efficiency and/or overall power output of the turbocharger may be greater than the supercharger.
If the supercharger is not one that can be driven by means of an electric machine, that is to say electrically, a mechanical or kinematic connection for power transmission is generally needed between the supercharger and the internal combustion engine, which also influences the packaging in the engine bay.
The benefit of a supercharger in relation to an exhaust-gas turbocharger consists in that the supercharger can generate, and make available, the desired charge pressure at a greater range of times, specifically regardless of the operating state of the internal combustion engine. This applies in particular to a supercharger which can be driven electrically by means of an electric machine, and is therefore independent of the rotational speed of the crankshaft. For example, the supercharger may provide charge pressure during transient conditions where the turbocharger may lag.
In previous examples, it is specifically the case that difficulties are encountered in achieving an increase in power in all engine speed ranges by means of exhaust-gas turbocharging. A relatively severe torque drop is observed in the event of a certain engine speed being undershot. Said torque drop is understandable if one takes into consideration that the charge pressure ratio is dependent on the turbine pressure ratio or the turbine power. If the engine speed is reduced, this leads to a smaller exhaust-gas mass flow and therefore to a lower turbine pressure ratio or a lower turbine power. Consequently, toward lower engine speeds, the charge pressure ratio likewise decreases. This equates to a torque drop.
The internal combustion engine to which the present disclosure relates has a compressor for supercharging purposes, wherein, in the context of the present disclosure, both a supercharger that can be driven by means of an auxiliary drive and a compressor of an exhaust-gas turbocharger can be subsumed under the expression “compressor”.
An issue in the case of supercharging is that the charge air heats up during the compression in the compressor, whereby the efficiency of the compression deteriorates. The compressed hot charge air is duly generally cooled downstream of the compressor in a charge-air cooler of the intake system to ensure an improved cylinder charge. That is to say, compression by cooling may occur, thereby allowing more compressed air to flow to each cylinder of the engine if desired. However, owing to the operating principle, said charge-air cooling has no influence on the compression of the charge air in the compressor that is performed upstream.
To reduce or eliminate efficiency losses during the compression, compressors according to previous examples are cooled. In general, the compressor housing may be equipped with at least one coolant jacket to form the cooling arrangement. Either the housing is a cast part, wherein a coolant jacket is formed as an integral constituent part of a monolithic housing during the course of the casting process, or said housing is of modular construction, wherein during the course of the assembly process, a cavity is formed which serves as coolant jacket.
From the previous examples, concepts are known in which a coolant jacket is provided in the outlet region of the compressor, and concepts are also known in which the coolant jacket follows the contour of the impeller. Both concepts are unsuitable for effectively cooling the charge air during the compression in the compressor and for ensuring as isothermic a compression as possible and thereby improving the efficiency of the compression.
Consequently, further or other measures may be desired to improve the efficiency of the compression in a supercharged internal combustion engine.
In one example, the issues described above may be addressed by a supercharged internal combustion engine having an intake system for the supply of a charge-air flow, an exhaust-gas discharge system for the discharge of exhaust gas, at least one compressor arranged in the intake system, which compressor comprises at least one impeller which is mounted, in a compressor housing, on a rotatable shaft, and a bearing housing for the accommodation and mounting of the rotatable shaft of the at least one compressor, which internal combustion engine further comprises that the rotatable shaft of the at least one compressor is equipped with a ventilation system which comprises at least one duct which is formed so as to be open to the intake system upstream of the at least one compressor and from which at least one line branches off which emerges from the shaft between the at least one compressor and the bearing housing. In this way, heat transfer from the turbine to the compressor is reduced and cooling to the compressor blades is increased.
As one example, the compressor of the internal combustion engine according to the present disclosure is air-cooled and has at least one ventilation system which is suitable for dissipating heat from the compressor and from the charge air situated in the compressor. For this purpose, the rotatable shaft of the compressor is equipped with at least one duct which is connected or at least connectable to the intake system upstream of the compressor and from which at least one line branches off which emerges into the surroundings.
The ventilation system according to the present disclosure is supplied by the duct with air from the intake system upstream of the compressor, wherein the air passes into the surroundings via lines which branch off from the duct. As it flows through the ventilation system, the air cools the shaft of the compressor. Here, in particular, the convection between the rotating shaft and the air flow is utilized for the heat transfer and the heat dissipation.
The air which heats up during the compression is to be regarded as a heat source, wherein the temperature difference between the hot air and the relatively cool or cooled compressor shaft drives the heat dissipation. According to the present disclosure, the heat is extracted from the compressor and the shaft by means of air as said air flows through, and said heat is dissipated to the surroundings by the ventilation system.
By means of the approach according to the present disclosure, the charge air can be cooled during the compression, wherein an isothermic compression is sought, which is distinguished by particularly high efficiency.
The internal combustion engine according to the present disclosure may be a supercharged internal combustion engine which is improved in relation to previous examples with regard to the efficiency of the compression of the charge air in the compressor. The object on which the present disclosure is based is thereby achieved and air is cooled during compression more than in the previous examples utilizing coolant jackets in the compressor housing or the like.
The concept according to the present disclosure for cooling the charge air is also distinguished by the fact that it is suitable for retrofitting of compressors already on the market. Said another way, the cooling arrangement of the present disclosure is relatively simple to introduce to current turbocharging systems and turbocharging systems already in use. Thus, the manufacture of the cooling arrangement is relatively simple compared to, for example, arranging a cooling jacket in the compressor housing.
The at least one impeller of the compressor may be fastened rotationally conjointly to the shaft.
Additional embodiments of the supercharged internal combustion engine will be discussed below.
Embodiments of the supercharged internal combustion engine may comprise in which the at least one duct opens into the intake system at a compressor-side end side of the shaft. Then, the at least one duct faces toward the charge-air inflow in the inlet region of the compressor, and the flow energy can be utilized for feeding air into the ventilation system and conveying said air through the ventilation system.
Embodiments of the supercharged internal combustion engine may comprise in which the at least one duct is of rectilinear form. A rectilinear form of the duct facilitates the manufacture of the duct, for example by means of drilling.
In this context, embodiments of the supercharged internal combustion engine may comprise in which the at least one duct runs coaxially with respect to the shaft or with respect to the axis of rotation of the shaft. Thus, air from the intake system may readily flow into the ventilation system without turning or deviating from an original direction of flow.
Embodiments of the supercharged internal combustion engine may comprise in which the at least one line is of rectilinear form. A rectilinear form of the line facilitates the manufacture of the line, for example by means of drilling.
In this context, embodiments of the supercharged internal combustion engine may comprise in which the at least one line runs perpendicular to the at least one duct. Then, when the shaft is in rotation, the centrifugal force acting on the air situated in the ventilation system can be utilized without hindrance for conveying the air in the ventilation system or out of the ventilation system. This is supplemented by a pump effect which results from the pressure gradient across the ventilation system. The higher the air throughput and thus the flow speed of the air in the ventilation system, the greater the amount of heat that is dissipated.
In this context, embodiments of the supercharged internal combustion engine may further comprise in which the at least one line is oriented radially outward. In one example, the at least one line functions as an outlet, expelling air out of the ventilation system and into a space in the turbocharger housing.
Embodiments of the supercharged internal combustion engine may comprise in which at least two lines are provided.
Embodiments of the supercharged internal combustion engine may comprise in which multiple lines are provided, but only one duct.
Embodiments of the supercharged internal combustion engine may comprise in which, furthermore, at least one disk-shaped element is arranged on the shaft, preferably at the compressor side. A disk-shaped element has a relatively large surface in contact with the surroundings, whereby the heat dissipation to the surroundings is increased or improved.
When the compressor is in operation, the disk-shaped element rotates with the rotating shaft, whereby the heat transfer from the disk to the surroundings may be assisted by convection.
Embodiments of the supercharged internal combustion engine may comprise in which the shaft has, at the impeller side, a thickened shaft end for accommodating the at least one impeller.
The thickened shaft end facilitates the introduction of heat or heat transfer from the impeller into the shaft and thus the heat dissipation from the charge air situated in the compressor. Furthermore, the thickened shaft end increases the strength of the shaft and allows for the fact that, according to the present disclosure, the shaft is equipped with a ventilation system, that is to say with cavities.
Embodiments of the supercharged internal combustion engine may comprise in which at least one compressor which can be driven by means of an auxiliary drive is arranged in the intake system.
A compressor which can be driven via an auxiliary drive, that is to say a supercharger, can generate and make available the desired charge pressure at a wide range of engine operating parameters, specifically independently of the operating state of the internal combustion engine. This applies in particular to a supercharger which can be driven electrically by means of an electric machine, and is therefore independent of the rotational speed of the crankshaft. For example, the supercharger may provide the desired boost during transient conditions where engine exhaust gas output may be too low to sufficiently drive a turbine.
In this context, embodiments of the supercharged internal combustion engine may comprise in which the at least one compressor of the internal combustion engine is a compressor which can be driven by means of an auxiliary drive.
Embodiments of the supercharged internal combustion engine may further comprise in which at least one exhaust-gas turbocharger is provided, which comprises a turbine arranged in the exhaust-gas discharge system and a compressor arranged in the intake system.
In this context, embodiments of the supercharged internal combustion engine may comprise in which the at least one compressor is the compressor of the at least one exhaust-gas turbocharger.
To be able to counteract a torque drop at low engine speeds, embodiments of the internal combustion engine may comprise in which at least two exhaust-gas turbochargers are provided. Specifically, if the engine speed is reduced, this leads to a smaller exhaust-gas mass flow and therefore to a lower charge-pressure ratio.
Through the use of multiple exhaust-gas turbochargers, for example multiple exhaust-gas turbochargers connected in series or parallel, the torque characteristic of a supercharged internal combustion engine may be increased.
To improve the torque characteristic, it is also possible, in addition to the at least one exhaust-gas turbocharger, for a further compressor, that is to say a compressor which can be driven by means of an auxiliary drive, to be provided.
Embodiments of the supercharged internal combustion engine may comprise in which the at least one impeller has a multiplicity of impeller blades to improve the heat dissipation.
Embodiments of the supercharged internal combustion engine may comprise in which the at least one compressor is a radial compressor. This embodiment permits dense packaging with regard to the supercharging arrangement. The compressor housing may be configured as a spiral or worm housing. In the case of an exhaust-gas turbocharger, the diversion of the charge-air flow in the compressor of the exhaust-gas turbocharger may be utilized for conducting the compressed charge air on the shortest path from the outlet side, on which the turbine of the exhaust-gas turbocharger is commonly arranged, to the inlet side.
In this connection, embodiments may comprise in which the turbine of the at least one exhaust-gas turbocharger is a radial turbine. This embodiment likewise permits dense packaging of the exhaust-gas turbocharger and thus of the supercharging arrangement as a whole.
By contrast to turbines, compressors are defined in terms of their exit flow. A radial compressor is thus a compressor whose flow exiting the rotor blades runs substantially radially. In the context of the present disclosure, “substantially radially” means that the speed component in the radial direction is greater than the axial speed component.
Embodiments of the supercharged internal combustion engine may further comprise in which the at least one compressor is of axial type of construction. The flow exiting the impeller blades of an axial compressor runs substantially axially.
Embodiments of the supercharged internal combustion engine may comprise in which the at least one compressor has an inlet region which runs coaxially with respect to the shaft of the at least one impeller and which is designed such that the flow of charge air approaching the at least one impeller runs substantially axially.
In the case of an axial inflow to the compressor, a diversion or change in direction of the charge-air flow in the intake system upstream of the at least one impeller is often omitted, whereby unnecessary pressure losses in the charge-air flow owing to flow diversion are avoided, and the pressure of the charge air at the inlet into the compressor is increased.
Embodiments of the supercharged internal combustion engine may comprise in which the ventilation system is equipped with a shut-off element which in the open state opens up, that is to say activates, the ventilation system and which in the closed state shuts off, that is to say deactivates, the ventilation system.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.